Particles leaving the surface of a bed of particles have positive and negative charges due to their environmental factors, particle physical parameters and geometric parameters, so that the amount of the charge of each particle varies. However, because currently there exists no measurement instrument to provide a direct measurement of charge amount of particles leaving the particle system, and therefore it is impossible to directly measure the charge amount of particles leaving the particle system, further to verify such charging mechanism, meanwhile to analyze effects of environmental factors, particle physical parameters and geometric parameters to the charge.